基本思路是“大”的數排前面，比如’9’>‘87’

再者是‘42’和‘420’的比較，‘42420’>‘42042’,如果只是單純地在’42’後加’2’變成442>420，這樣會遇到另外一個問題就是‘42’和‘422’的比較，‘42422’>‘42242’。python2裡有cmp，python3裡移除了。所以先用了‘42’*2和‘422’*2這樣的變換。又遇到了問題，‘42’和‘42421’不符合。所以不能簡單地擴充套件一倍，要擴充套件成最長的字串的長度。

class Solution:
    def largestNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: str
        """
 

        nums = [str(x) for x in nums]
        maxL = max([len(x) for x in nums])
        nums.sort(key=lambda x: x*(maxL//len(x)+1), reverse=True)
        if nums and nums[0] == '0': return '0'
        return ''.join(nums)

class Solution(object):
    def largestNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: str
        """
 

        def mysort(list1):
            maxL=len(max(list1))
            tmp = []
            for s in list1:
                ls=len(s)
                if ls==maxL:
                    tmp.append([s,s])
                else:
                    sortK = s+s[0]*(maxL-ls)
                    if len(sortK)
 
>=2 and sortK[-2] > sortK[-1]:
                        f=0
                        for index in range(len(tmp)):
                            if tmp[index][1]==sortK:
                                f=1
                                break
                        if f==1:
                            tmp.insert(index,[s,sortK])
                        else:
                            tmp.append([s,sortK])
                    else:
                        tmp.append([s,sortK]) 
            a=sorted(tmp,key=lambda tmp:tmp[1],reverse=True)
            strkey=''
            for k in a:
                strkey+=k[0]
            return strkey
        res=''
        dict1={}
        zeros=0
        for i in range(1,10):
            dict1[i]=[]
        for n in nums:
            if n==9:
                res+='9'
            elif n==0:
                zeros+=1
            else:
                dict1[int(str(n)[0])].append(str(n)) 
        for j in range(9,0,-1):
            if dict1[j]==[]:
                continue
            res+=mysort(dict1[j])
        res=res+'0'*zeros
        return '0' if res[0]=='0' else res